Apple Business: Can't add device or download from App Store

I'm a new administrator of a new Apple Business account. I'm trying to figure out how to set up managed devices, but I can't download any apps from the Mac App Store, including the Apple Configurator. I get this error: "This feature isn't available with the Apple ID you're currently using."

How can I allow my Apple Business Managed Apple ID to use the App Store? There's nothing in the Apple Business portal that shows that the App Store would be disabled.